World on Fire
by ValkyrieVeela
Summary: Based on the 'World on Fire - Dark Merlin & Morgana' YouTube video by BlacksGodDaughter. Basically, Merlin has a change of heart. Rated T to be safe. Haven't actually asked permission to post this but will anyway, so be aware there's an authorised fic on another site (link in video description). Posting this at 1:05 am so don't expect awesomeness.


**21.12.15, Mon**

 **A/N: Went crazy because lactose intolerance brings out Violent Me, so watched all my favourite YouTube videos in an effort to distract myself and now desperately need write intense angsty fanfiction to reflect the inner darkness of my soul.**

 **:)**

 **So this is based on 'World On Fire' (the fan video) and is, in my head because Uther's in it, set basically at the beginning of Series 4, if Series 4 was happening at the time Series 5 did, i.e. when Mordred is old enough to join the Knights (and he has). No Agravaine because he's _not_ in it and another character basically fulfills his function anyways.**

 **Here's the story given in the video summary - SPOILER ALERT!**

Storyline: Morgana discovers Merlin's secret but promises to keep it even after becoming an enemy of Camelot. While on a quest with Arthur, Morgana confronts Merlin and asks for him to join her in taking down Camelot - Merlin originally says no but realizes that he will always be an outcast and looked down upon. The night he returns to Camelot with Arthur, he returns to the woods and finds Morgana. From that day on Merlin brings inside news to Morgana about traps and the war against Magic. The more Merlin and Morgana work together the more powerful Merlin feels, and him and Morgana poison the king. Gaius is suspicious and confronts Merlin. After Merlin and Morgana wage war the night of Arthur's coronation, Gaius realizes it has gotten out of hand and is about to tell Arthur when Merlin uses his powers to remove all of his and Morgana's army. In the aftermath of the battle, the Knights are attacked by a curse - at this point Gaius does tell Arthur. Arthur and the Knights surround Merlin in the forest and are then confronted with the truth - Merlin is a sorcerer, not just a spy. Morgana and Merlin return to Camelot and take over the castle - Merlin stays behind to make sure it is empty will Morgana forces Arthur and his Knights out towards Camlan. The next morning Merlin and Morgana attack and kill Arthur.

* * *

World On Fire

"I do understand how you must feel, Merlin."

His eyes were a darker shade of blue now. They always were when he cried. He looked up at his mentor, for once allowing him to see the true depths of his pain.

"You could never understand."

* * *

He held up his hand to see further in the pitch black of the tunnels. He spoke the spell, needing to hear a human voice in the crushing silence.

" _Leoht_." He scrambled backwards, tripping over his own feet in the process. He fell with a thud, gaping up at her.

" _Merlin?!_ " Her hair was more tangled than he remembered, her dress more torn. She was thinner than when he'd last seen her and everything about her was black and white - fitting, given her outlook on the world had always been so. But - she had a little green, too, he saw.

And evil. That, too.

"What the bloody hell do you think you're _doing?!_ " _Get her off guard, distract her, make her forget, please please please-_ "You're a witch and an outlaw - and you're running around in Camelot's siege tunnels! _Why?!_ "

She pursed her (thinner) (paler) lips.

"Don't think I'm stupid enough to fall for your act now, Merlin. I know what you're trying to do!"

"Well - _I_ know what _you're_ doing!"

"Of _course_ you do, _Mer_ lin, I'm a known traitoress! The real question is - what in blazes do you think _you're_ doing? We could have been working together all this time, you fool! You could have _helped_ me - hell, you could've helped me even if you weren't - you know."

"I have no idea what you're talking about." He said it so stiffly that she gave a sigh and her shoulders slumped.

"Are you going to make me spell it out?"

"I have no - I - I don't-"

"Your secret's safe with me."

"... My secret?"

She pointed at the witchlight in his hand.

"Ah. That."

"You're a bloody fool, Merlin. Do you think Arthur would tolerate you for one minute if he knew the truth-"

"-Morgana-"

"-Sorcerer?!" He winced.

"Warlock."

"...What?"

"Warlock...? It's _warlock_ , I'm a - never mind. Look, Morgana, I - there's this prophecy about the return of magic, which Arthur and I are supposed to bring about together and, well, you're kind of ruining it, and-"

" _Excuse_ me?!"

"Basically, it all comes down to you leaving Arthur and Camelot alone while I fix everything. _We can find another way_ , Morgana." There was a pause.

"No, Merlin. We can't." She sounded so lost and alone and so awfully _tired_ that he just stared after her as she walked away from him into the darkness.

* * *

"Arthur, he saved your _life -_ saved all our lives! Sorcerer or not, he deserves a bloody medal for bothering, you clotpole, not the noose - or gods forbid, the pyre!"

"...'Gods', Merlin?" The manservant froze. Only pagans swore by multiple gods. Good, Christian citizens of Camelot did not. Not if they wished to keep their heads.

"Slip of the tongue. I've had a funny anti-lisps since my colds." He mechanically rolled his eyes and grinned, praying - to the _gods_ \- that Arthur wouldn't notice the strain.

Arthur gave it another few seconds before curling the corners of his mouth and pretending it hadn't been a serious accusation. Both sides of the coin knew better than to believe it.

They continued talking until Arthur sent Merlin off on some errand of paperwork delivery, neither party wishing to remain in the other's company for long. Merlin scurried off to the dungeons to hand over the sheet of parchment, ink still wet when he got there. Having dropped it on the guard's table he turned to leave.

"Ha - ta, Merlin! This is excellent!" Merlin swivelled round, plastering on a politely curious expression.

"What is, Haldir?"

"Execution permit, you ninny!" Not noticing how Merlin's face had glazed over, the guard continued. "'Death by fire' - always brings in a good crowd, eh? Kids love it. Brings in a bonus for my lot - w'can sell food for roasting and festival garlands and souvenirs - right moneyspinners, executions!"

"Souvenirs?" Merlin asked faintly.

"Yeah, y'know - hair, toes, teeth, fingers - you name it! Don't matter what state he's in, s'long as he's alive to scream, eh?" Finally noticing Merlin's rigid stance and paling complexion, Haldir - who was a Mercian by birth, Merlin remembered suddenly - took pity on him. "Sorry, mate, I know you'm a bit squeamish about executions. You're Gaius' boy as well as the Regent's, right? More up to healing than harming."

Merlin gave a stiff nod and fled.

* * *

Alone in his room, he sobbed as quietly as he could. Chills were running down his back violently. This place, once so full of light, was starting to show its true colours more and more with each step he took into the shadows.

It wasn't home any longer.

* * *

 _Knock knock._

Morgana froze.

 _Knock-knock-knock._

She slowly, silently turned her head to face the door of her hovel...

BANG! BANG! BANG!

She gave an involuntary yelp.

"For the gods' sake, Morgana, I know you're in there! _Let me in_ or I'll - oh. Hello." He added the last word somewhat sheepishly as the door swung open, leaving his curled fist poised to strike the witch in the face. Noticing her pointed glance, he stuffed the offending limb into his satchel and removed an artfully chosen wildflower bouquet. "For old times' sake. Since I'm not here to kill you. Thought it was only polite."

She frostily took the flowers from him.

"Next time," he winced at the icy tone, "just say 'Hello' before you decide to scare the living _daylights_ out of me with all the banging and the yelling."

"Right. Yes - sorry. Although, to be fair, I did knock fir- I'll be quiet now." Her glares were notorious for a reason, he decided. Softening at his display of compliance, she asked more gently,

"Not too quiet, I hope. You have yet to explain why you're here. This -" she wafted the flowers about "- is a metaphorical white flag. It symbolises a temporary truce between us - _Emrys_." He gaped.

"You _have_ been doing your homework." She smirked.

"Of course. Which begs the question - why are you here? Surely this is a betrayal of your _dear_ Arthur?" Merlin's face instantly closed off. Feathers ruffled by this reaction, Morgana decided to test the waters. "Ah - perhaps not _quite_ so dear after all?" Getting no reaction, she dropped the teasing tone. "Has something happened, Merlin?"

He managed to stay still for a moment, before releasing an enormous sigh and running his hand through his hair. Unsure of quite what that meant, Morgana offered him a chair and began to make nettle tea to give herself something to do.

"He's out of control." She paused as she set a cup in front of him.

"What do you mean?" She asked carefully. "I haven't heard anything about him running rampage. There's no news of a second Purge on the horizon - "

"I mean he's out of _my_ control." Seeing the astonishment on her face, he gave a small smile and elaborated. "You know Arthur. A real sheep when it comes to it - always ripe for moulding and guiding." He sighed. "I thought at first that he was my friend. That he would come round because it was the right thing to do - but I now know that it was an impossible dream. I was his best friend - we keep up the charade even now - but before I came along he'd had twenty years of indoctrination from his father and everyone around him. You helped, of course, but one person among thousands is hardly enough, especially when he viewed you as a sister and did the opposite of all you did simply on principle."

"He helped us with Mordred." She played Devil's advocate to see where he was going with this. "What's changed?" No, it was something else, something... Ah. "Merlin, what did he _do_?" He pinched his nose in frustration.

"He's started executing sorcerers." Puzzled, she replied,

"But surely he was doing that anyway-?"

" _No_." The sharpness of his answer startled her. "I truly thought he'd be a passive regent, purely administrative, but - it's like he's using it as an opportunity to do everything his father would approve of. It's almost like he thinks it'll bring Uther back."

"What?" He gave her a suspicious look.

"Surely you've heard how Uther's mind has left him? How Arthur's been crowned Prince Regent while Uther is hidden away in his chambers, staring into space and insane with grief?" His words were biting, accusing, and she realised that her betrayal must have been the cause of Uther's madness.

"I hadn't heard any of that."

"What have you been _doing_ these past three years?"

"Tending to my sister in Cornwallum, our homeland. She just passed last winter."

"... I'm sorry."

"No, you're not."

"I'm sorry _for your loss_."

"... Thank you."

They sat in silence for a moment.

"What will you do now?"

"Morgana, I'll do whatever it takes. I can't just stand by and watch him kill us all off one by one." She smirked.

"That's good. Do you plan on joining me then?"

"If you'll have me."

"Well, there is one little issue we've not yet discussed..." He sighed.

"I poisoned you."

"You did."

"I've said sorry more times than I can count, Morgana! You know full well Morgause left me with no choice - and you know I knew Morgause could use her power as a High Priestess to save you even if the antidote failed!" She raised an eyebrow. "I'm _sorry_ , Morgana."

"Okay, _now_ you can join." They smirked at each other.

"When do we start?" She pushed his cup towards him.

"When you've finished your tea."

* * *

"Well? What news?"

"It's a trap - the trading cart you're after, they're sending a decoy by the old route and they're sending the real caravan through the Valley of the fallen Kings."

"Just two miles south of here - excellent."

"Happy to help, my lady."

"A pleasure doing business with you, my lord."

* * *

"Emrys?"

"Sh! It's alright - we're getting you out. _Tospringe!_ Follow me - hurry!" They escape the dungeons with ease. Merlin takes them to the forest.

"Thank you, my lord, thank you!"

"It's alright - now follow that path west until you find a cottage. It's camouflaged and dark, so call out for help once you've travelled three miles. You'll be met by a High Priestess - she'll take you to the nearest camp."

"A High Priestess?" The mother and daughter in Druid robes were wary now. "You don't mean-"

Merlin caught their hands in his.

"Please, please believe me - she's not what she was. She wants what I want, prophecies notwithstanding - Arthur is no longer destined to save us. It's just me now, and she's willing to help." He looked them in the eyes. "Are you?"

After a pause, they nodded fervently.

"Yes, Emrys. We are." He smiled.

"Thank you."

* * *

As they knocked their cups together in celebration, the mulled wine a rare treat on their lips, Merlin and Morgana laughed in exhilaration.

"Finally free from that monster!"

"Thousands of deaths avenged!"

"And thousands more prevented, gods willing!"

They danced and sang that night, lighting a bonfire outside and cackling madly through the flames. Later that week, they revived that very fire to burn Uther's body on after they stole him from his burial chamber. The soon-to-be-King never noticed the loss of his father's body - he was far too busy trying to discover who had laced Uther's final cup of water with hemlock.

* * *

"Merlin, we need to talk." Merlin smiled jovially.

"What about, Gaius?" Pursing his lips, Gaius answered,

" _That_."

"What?"

"The whole of Camelot is in mourning, and yet you run around grinning like a loon in your brightest clothing. Have you _no_ respect for your own life or are you foolish enough to believe fingers will not start pointing at you when the killer is not found?" Merlin sobered quickly. "That's better. Now answer me, boy!"

"What do you mean, _when_ the killer is not found?" Gaius glared at him.

"I'm no fool, Merlin. I saw you take the hemlock from my stores. I know you had access to Uther's food and drink - and I know how hard it has been for you to save his life in the past, yet you've done it anyway. Why would you do something like this, Merlin? Why? This isn't like you. This is cruel and cold and everything I know you are not - in fact, this whole situation reeks of Morgana. It was hemlock you gave her all those years ago, wasn't it?" Receiving no answer, he made one last desperate plea. "Will you at least tell me what's _wrong_?"

Merlin stared at him in silence for a moment, then gave a hollow laugh.

"Something deep inside," he murmured, "and when it came for me I felt this emptiness... I couldn't breathe."

Gaius stared at the man he barely recognised as his ward.

"What happened to the young boy who came into my chambers just a few years a go?" Stonily Merlin snapped,

"He grew up."

* * *

Merlin lounged idly against a column in the Great Hall. Arthur's coronation had been nothing special - the crowd had yelled _Long live the King!_ with more fear then gusto, and the feast was full of dark looks and mutterings under the cover of merriment. Arthur himself was slumped in his seat, pouting and twirling his goblet - which Merlin hadn't bothered to refill and intended to leave empty for the rest of the night. After all, he had more important work to do that night than care for his drunken slob a a King.

No-one noticed him slip out of a side door, though he'd brought a empty pitcher as an excuse just in case. His escape into the woods went similarly unnoticed, though his arrival at Morgana's camp was an entirely different affair.

"Merlin!" She rose from her seat at the final war meeting and greeted him with a hug. "I trust you got here safely?"

"Of course." He smiled.

"Are you ready?"

"Oh, yes." They exchanged smirks and Morgana dismissed her generals with a wave of her hand. The pair left the tent and made their way to the front lines.

"Do you think...?" Merlin nodded.

"It's time." He spoke the spell to reveal their army. Howling and whooping, they marched on Camelot.

* * *

Watching from a window, Gaius spied the torches of an army flicker into life across the city on the plain. His eyes widened in horror as he heard the howling.

"'Let loose the hounds of war'," he whispered. As he watched, he saw balls of fire fly in an arc through the sky. "'Let the dread fire of the last Priestess rain down on angry skies.'"

Snapping back into reality, Gaius began rushing to the infirmary. It looked like he would be needed - soon.

* * *

Merlin signalled to Morgana that he was about to leave. When she nodded her assent, he began making his way back to Camelot. In order to maintain his cover and therefore be in the right place to perform the final spell, he would need to return in the next fifteen minutes or so.

He began running.

* * *

"Merlin! Where have you _been?_ " Panting and placing his hands on his knees, Merlin gasped,

"Got stuck in the stampede in the Great Hall - m'fine, though, Gwen, just out of breath. You wouldn't believe how fast the knights move when they hear 'Sorcerers!', honestly!" Gwen gave a puzzled little smile. "What?"

"I didn't see you in there..."

"Yeah, but I was at South corridor, just coming back from refilling a pitcher. Actually, I suppose I was _already_ out of the Hall by a few feet-" Gwen laughed.

"Doesn't matter - you alright now?" He nodded. "Good, because we've already got burn wounds coming in from the West wall..."

* * *

Frowning, Gaius watched Merlin's conversation with Gwen from across the room. He was the only one to see the smirk flash across Merlin's lips as Gwen turned to lead him to the first patients.

Suddenly, Gaius understood what it meant.

"You foolish, _foolish_ boy!"

* * *

After a few hours, Merlin slipped out of the infirmary. Gaius took the opportunity to leave as well, as he hadn't dared to go to Arthur until Merlin was in the middle of committing treason. That was the only way he could think of to persuade his King of Merlin's guilt. He hadn't got far, however, when the King found him instead.

"Gaius! What are you doing away from your post?"

"I'm sorry sire, I-"

"Never mind that - I need you to tell me how many men are lost and how many are ready to go back into the field." Sagging with defeat, Gaius resigned himself to the fact that the battle would never be won with Emrys opposing them.

"It matters not."

"What?! What are you talking-?!"

"There's no escape, Arthur."

"Sire!"

"What is it, Leon?"

"Morgana's army, sire - they've - well-"

"Spit it out, man!"

"They've vanished! It's the work of _sorcery_ , sire - one moment they were there, then the next - poof!"

"'Poof'?"

"Poof!"

"'Poof'...? Sounds like nothing I've ever heard of, sire. A true transportation spell mimics a whirlwind, and an invisibility spell is silent as the grave - quite specifically so, in fact - but I can honestly say I have never in my life heard of a vanishing spell, much less one that goes 'poof!'" _Though if anyone were to invent it, I'd bet my life it was Merlin! What_ are _you up to?_

"No-one cares, Gaius."

"Yes, sire."

* * *

There was one last spell for Merlin to perform before the night was done. Rushing back to Gaius' chambers, he began preparing the circle and the ingredients. He was about to complete the incantation when Gaius himself hobbled into the room as fast as he could. Gasping for breath and leaning on his bench he sank into his seat as he realised what ritual it was that Merlin had almost finished.

"Please, do not do this."

With a few whispered words and a flash of his eyes, Merlin's spell was done and tidied away, leaving no trace of his involvement.

"I had no choice."

* * *

"Gaius-"

"I fear for Camelot." Hands clasped in front of him and head bowed, Gaius stood before the King in the royal chambers, hoping and praying with every fibre of his being that he would be taken seriously, that he would not be too late.

"So you believe there's a traitor in Camelot."

"Yes."

"Do you have any idea who?" _Deep breath._

"I'm afraid I now know for certain, sire, after the discovery of the knight with a mutilated face to show Morgana's formal declaration of war."

"Then tell me."

"I - the - the traitor is - oh, sire, I _am_ sorry - the traitor is Merlin. I can offer you proof - magical artifacts hidden in the floor of his bedroom, along with magically produced copies of secret plans and official documents-"

"That won't be necessary."

Arthur landed in his chair with a heavy _thud_. He was dazed - he'd known it wasn't exactly brilliant between him and Merlin, known that he'd almost begun to suspect him himself on numerous occasions - and yet, this was somehow the ultimate betrayal.

"Ask the knights to prepare. Merlin will report to Morgana tonight, I'm sure - it's what I'd have a spy of mine do. We'll follow him and bring him in for questioning. If he struggles, tries to escape..."

Gaius bowed his head, knowing that they would never actually be able to kill Merlin. He still held out hope that Merlin would come back to them if only he could see how much it hurt his friends - at least, that's what he told himself in order to justify keeping one last secret for his very much ex-ward. He'd betrayed Merlin's lover to Uther and his newfound allegiance to Arthur - he couldn't quite bring himself to actually betray Merlin's magic to Camelot's King, no matter the circumstances.

* * *

Merlin was buzzing with excitement as he left Camelot that night. With the new positioning of the army, it would be child's play to drive Camelot's knights to the plain of Camlann where the other half of their own men would trap the enemy and massacre them. He wasn't normally so violent-minded, but the day before the coronation he'd had to witness the drowning of a three-year-old girl and he was in the mood for revenge.

 _Snap_.

"Stay where you are, _traitor_." Arthur was the one who spoke. Merlin's maniacal grin dropped from his lips and his expression became cold, calculating. He spun in a slow circle, casually noting the men. There was Arthur, of course, Leon, Gwaine, Percival, Elyan, four or five relative strangers, and - Mordred? Interesting. The boy's expression seemed to be one of cautious curiosity. Merlin tilted his head as he studied him. Hearing the crunch of the leaves, he remembered the others.

"If you value your lives," the corner of his mouth almost twitched at the wideness of Mordred's astonished eyes, "you won't take another step." He paused, then spoke directly to Mordred. "You're going to have to choose, you know. They won't win - not with me against them. You can run or you can fight, but you cannot be a Camelot knight." He spoke softly enough that only the inner circle of knights could hear him. The airy sing-song tone seemed to disturb his old friends, but Mordred's face now displayed only understanding. One of the knights he didn't know, too far away to hear his offer, called out,

"You don't even have a sword!" Merlin sighed and raised his voice again to quip, somewhat acidly,

"I don't _need_ one." Then, with a single flash of his eyes, several things happened at once.

First, all of the knights but Mordred cried out in surprise as they hadn't been expecting a sorcerer. Then the strange knights were thrown back into unconsciousness and out of the way. Next, a ring of fire five feet high sprang up to surround the knights on each side as their swords - all but Mordred's - were flung out of their hands.

"What happened to you, Merlin? I thought we were friends." With a noise of disgust, Merlin sneered,

"Well, you were wrong, Arthur." Turning to leave through the path he'd made through the circles, he was stopped by something unexpected.

"Wait! Wait, Emrys, I - I can't fight my friends, but if you'll allow me-"

"What?"

"I'll go with you, my lord."

"Why?"

"I do not wish to die." After studying him for a moment, Merlin nodded.

"Anyone else?"

"What the hell are you doing, Merlin?"

"Saving lives, Gwaine. Saving lives. Will you help me?"

"I - you-"

"Yeah, had a funny feeling you'd say that. Well, I can kill you now if you like. Save you the trouble of dying in battle - so _messy_. Same goes for the rest of you, of course - except Arthur. _That_ would be ridiculous." He looked round at them all one more time. "What? No-one to take my offer? Well, it's hardly a first. I'll try and spare you in battle, if I see you - well, I won't, that's a lie, but I will try to save Gwaine because he's my favourite. Coming, Mordred?" He opened a gap for the ex-druid to step through. "Oh, and if this is a clever ploy to kill me, I'm immortal, so..."

"I know, my lord. That's what 'Emrys' means."

"Clever lad." Merlin clapped him on the back and led him away.

* * *

The fires had died down within an hour of their departure. It had taken a lot of persuading to get Arthur off his knees and back to Camelot.

Having reached the citadel they could only gaze on in horror as they watched Morgana's - and Merlin's - army begin to drive their own towards the pass they knew to be a veritable slaughterhouse.

"I made a terrible mistake." No-one could tell if he was talking about trusting Merlin or provoking him into switching sides. Perhaps he meant both.

* * *

Gaius watched from his makeshift infirmary. The final battle of the war was bloody. He watched as Percival and Elyan were cut down. He saw a huge Saxon behead Leon in an effort to get at Arthur - who beheaded the huge warrior in turn, not yet seeing the body of his friend. Gwaine's attackers were scorched off the face of the earth by Merlin's lightning, as promised - he made it to Gaius in time for his life to be saved, though he would have a huge knotted scar slashing down his chest and neck. The battle had begun at dawn, and was well over by noon. Arthur had been cut down by Merlin himself ("The prophecy said 'a druid' and I'm basically their God, so I must count") and after his death the remaining knights had been rounded up and systematically sorted into two groups: those willing to accept magic and those too bigoted to understand what they were being asked. The members of the latter group were killed. Gaius himself and his little healer's tent were captured and ordered to buck up and accept the new world order so that everybody could get on with their lives. After all, a Pendragon was on the throne, and wasn't that all that mattered, really?

Gaius didn't think so, but he didn't have the energy to fight it any longer. He simply sat down and recited a scrap of verse.

"'For brother will slaughter brother/ Friend will murder friend/ As the great horn sounds at cold dawn at Camlann/ The prophets do not lie/ There, Arthur will meet his end/ Upon that mighty plain.'"

* * *

 **Not entirely sure how I still managed to make this demi-crack, but oh well. You know, there's enough inspiration running round my head from this video that I could start a drabble series - not now though, obviously. I've been typing for about five hours straight (my computer had a hiccup and I had to rewrite a third of it) and I'm seriously exhausted. The dat at the top is wrong now because it's well past midnight. *sigh***

 **Never the mind, m'dearies, never the mind.**

 **PLEASE FOR THE LOVE OF ALL THE GODS EVER REVIEW**


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